Resistor



G. B. cRusE Nov. 3, 1931.

RESISTOR Filed Julyv 24, 1930 IIIIIIIIIHIIIIIIIIIIIIIIIIIIIIIIIII Fig INVENTOR Geary@ 5. Craase ATTO EY Patented Nov. 3, 1931 l UNITED STATES PATENT OFFICE GEORGE B. CROUSE, OF NEWARK, NEiW JERSEY, ASSIGNOR TO HARDWICK HINDLE, INC., OF NEWARK, NEW JERSEY, A CORPORATION OF NEW JERSEY RESISTOR This invention relates to resistors and more particularly to those of the tubular, vitreous enamel coated type.

In general a vitreous enamel resistor com- '54' prises a tube of porcelain or other refractory material, round the ends of which are clamped sultable contact bands of copper or other conducting material. The resistance wire, which is usually an alloy having high electrical resistance, is then wound on the tube between the Contact bands and riveted or otherwise attached thereto at its ends. The wound tube is then dipped or sprayed with the vitreous enamel slip and fired at such a temperature that the enamel becomes molten and flows over the entire surface of wire and tube. Ore or more coats of ena-mel, as required, are applied and fired over the original coat.

It is obvious that in a resistor of this type,

since the entire wire is coated with enamel, it is impossible to make any adjustments of the resistance value or to take o a contact at any point after the resistor is completed. -This feature is disadvantageous from several angles. In the first place, even through t-he original resistor is wound accurately to a specified resistance value, oxidation of .the wire will take place in the firing process, as a result of which the wire is reduced in crosssection and its resistance increased by an amount which is not accuratelvspredictable;-

secondly, in many applications of a resistor it is desirable to be able to change the resistance in service or to use the device as an adjustable potentiometer.

Man attempts have been made in the past to pro uce a resistor of the type to which this invention 'is directed, none of which have been conspicuously successful. Since the `finished enamel coating is very hard and brittle, it is impossible to satisfactorily grind is ofi' along the section in which it is desired to expose the wire, and, therefore, most ofthe i previous' 4attacks on the problem' were directed to exposing a track before firing. The common methodwas as follows: Before the w 'and resistorwas dipped or sprayed in the enamel slip, a shield, generally of adhesive tape, was laid along the resistor, the enamel thus being prevented from reaching the area which it was proposed to expose. The disadvantages of this method are twofold: In the first place, the fluid enamel in the furnace, during the firing process, has a very high surface tension and it therefore pulls back away from that area exposed. This produces a unit of very poor appearance and has other disadvantages, as will be seen immediately. Secondly, the wires are entirely exposed and unsupported in the slot. As a result of this, any form of sliding contact that may beused with the wires tends to displace them, bend them, and ultimately to break them.

The general object of this invention is to provide a resistor of the viterous enamel type having an area in which the wires are exposed so that contact may be made with them at any desired point of the exposed area. Except Where the Wires are exposed they are completely embedded in the enamel. The production of the resistor may be carried out in the usual manner and with the use of any other devices than those ordinarily employed in the production of resistors having their wires completely embedded.

This general object aswell as others which will hereinafter appear ist attained by forming in the form of the resistor a channel having a length and a width eqal to those of the desired track of exposed wire. The form is wound with wire and/enameled in the usual manner. When the enamel .becomes fluid in the firing process it pulls down into the channel leaving the wires exposed where they pass over the channel. By properly propertioning the depth of the channel, the density of the enamel slip, and the number of coats, it is possible to obtain an exposed track in which" the enamel surrounds the wires to a point slightly above the diameter of the wire.

the accompanying drawings in which Fig. 1 shows the tube of the resistor` Fig. 2 is a transverse view of the tube,

Fig. 3 is a view similar to' Fig. 1 showing the complete resistor,

Fig. 4 is a corresponding transverse view, Fig. 5 is an enlarged view intransverse section of the exposed track portion of the resistor, and

Fig. 6 is a corresponding longitudinal view `of a portion of the resistor.

^ copper or the like to which the ends of the wire are attached. The ends of the band extend outwardly to serve as terminals 5, are suitably fastened together and may, as shown in Fig. 4, carry a binding post 6 for connecjtion to an external circuit.

The resistance unit thus far described is then coated With enamel 7 in the usual manner and then fired. During this stage of manufacture the enamel becomes iluid and pulls down into the channel leaving the turns of wire exposed at their outer portions but with sufficient enamel between them as indicated at 8 in Figs. 5 and 6 to maintain the turns in their proper positions and prevent them from being displaced and possibly injured -when a sliding Contact device is used therewith. The above result requires the proper proportioning of the depth of the channel, the density of the enamel and the number of coats of enam'el. The channel should be relatively shallow as compared 4 ly adapted for use as the resistance unit of a rheostat of the slide wire type in which a movable contact device may be arranged to travel over the exposed track, as shown in my" copending application Serial Number 470,380, filed July 24, 1930, for resistors.

While a certain preferred embodiment of the invention has been disclosed, it will be understood that it may be embodied in other forms of resistors having exposed areas of various shapes and also that various changes in structural details may be made without departing from the principle of the invention as defined in the appended claims.

I claim:

1. .A resistor consisting of a refractory form having a channel therein, a wire wound upon the form and enamel on the form in which the Awire is embedded except at the channel where the enamel fills the channel whereby the outer portions of the turns of wire are vexposed over the channel.

2. A resistor consisting of a refractory tube having a-longitudinal channel in its outer.v portion, a wire wound upon the form and enamel on the tube in which the wire is embedded except at the channel where the enamel ills the channel whereby the outer portions of the turns of wire are exposed over the channel.

3. A resistor consisting of a refractory form having a channel which is relatively shallow as compared with its width and enamel on the form in which the wire is embedded exceptvat the channel where the enamel ills the channel whereby the outer portions of the turns of wire are exposed over the channel.

In testimony whereof I affix my signature.

GEORGE B. CROUSE.v 

